In many parts of the world due to inadequate rainfall it is necessary at certain times during the year to artificially water turf and landscaping. An ideal irrigation system for turf and landscaping should utilize a minimum number of valves, supply lines and sprinklers. Preferably the valves should be turned ON and OFF by an inexpensive, yet reliable electronic irrigation controller that is easy to program and can carry out a wide variety of watering schedules. The goal is to uniformly distribute the optimum amount of water over a given area. The type, placement and flow rates for each of the sprinklers are pre-selected when an irrigation system is designed and/or installed. The optimum flow rate provided by each sprinkler should preferably fall within plus or minus one-quarter gallon-per minute (GPM). The amount of water supplied by each sprinkler is largely determined by the size and configuration of its nozzle orifice(s), although variations result from fluctuations in water pressure that cannot be fully negated with regulators.
Residential and commercial irrigation systems typically include one or more solenoid operated valves that are turned ON and OFF by an electronic irrigation controller. The valves admit water to various subterranean branch lines usually made of PVC pipe that typically have several sprinklers connected to risers coupled to the branch lines at spaced intervals. Each combination of a solenoid valve and its associated sprinklers is referred to in the irrigation industry as a station or zone.
A modern electronic irrigation controller typically includes a microprocessor that executes one or more watering programs. The watering programs can be pre-programmed by the user via push button and/or rotary controls. The controller usually has an LCD or other display to facilitate programming by the user. Often the controller will revert to a default watering program in the case of a power failure. The microprocessor controls the solenoid valves via suitable drivers and switching devices. The valves are opened and closed by the microprocessor in accordance with the pre-programmed run and cycle times for each of the stations.
Over the past decade, modular expandable irrigation controllers have gained increasing popularity. In these controllers, the base portion of the system contains the microprocessor and user actuated controls. Each station is then controlled by a corresponding station module which typically comprises a plastic housing that encloses and supports a station module circuit, as well as wire connection terminals for connecting wires to a plurality of solenoid actuated valves. Usually each station module circuit includes a plurality of triacs or other AC switching devices and can independently control a plurality of solenoid actuated valves, i.e., stations. The station modules contain pins, sockets, card edge connectors or some other standard form of connectors for allowing them to be inserted into slots or receptacles in either the housing that contains the microprocessor or a separate back panel hinged to the microprocessor housing. When the station modules are plugged into a modular expandable irrigation controller they are mechanically supported and an electrical connection is made between the microprocessor and the driver. See for example, U.S. Pat. No. 6,721,630 B1 of Peter J. Woytowitz, assigned to Hunter Industries, Inc., the assignee of the present application.
The advantage of an irrigation controller with a modular expandable configuration is that the controller need only be equipped with the minimum number of station modules that can control the total number of stations needed. Thus, for example, an irrigation system may have only three zones, requiring only a single station module, while another may have twelve stations which might require four station modules. Considerable cost savings are thus achieved. Moreover, if an irrigation system expands after initial installation because the landscaping has increased, additional station modules can be plugged into the controller. The station modules can also be removed and replaced if damaged, for example, during a lightening strike. In some modular expandable irrigation systems the base unit is capable of controlling a minimal number of stations without requiring the addition of any station modules. In others, such as the ICC™ irrigation controller manufactured and sold by Hunter Industries, Inc., at least a power module and one irrigation station module must be plugged into the controller in order to operate any stations or zones.
Various manufacturers commercially produce modular expandable irrigation controllers. While the input controls and processor circuitry in these products vary in terms of their functional capabilities, the station modules do not. Conventional station modules include some kind of AC switch such as a triac, along with a circuit that can interpret commands from a microprocessor and drive the AC switch to the appropriate state. Some conventional station modules also include surge suppression components such as metal oxide varistors, gas tubes or inductors.
In conventional modular expandable irrigation controllers the division of tasks between the microprocessor and the station modules is consistent. The microprocessor handles user interface and schedules the irrigation. At the start time, the microprocessor sends a command to the appropriate station module instructing it to turn ON a particular station. Each station module receives and interprets commands and energizes or de-energizes the appropriate station output terminal. The microprocessor is burdened with monitoring currents for fault conditions, counting down the appropriate run time, and issuing the station OFF command when the run time has elapsed. In order for tasks such as current monitoring to be performed properly, the current flowing out of each station should be monitored as well as the total current. The total current must not exceed the rating of the transformer in the irrigation controller, and the current flowing out of each station module must not exceed the rating of the triacs. Where a modular expandable irrigation controller is capable of turning ON many stations simultaneously, the hardware and firmware capabilities of the microprocessor can be exceeded. The microprocessor then resorts to measuring only total current and/or limiting the number of stations that can be ON simultaneously.
Some conventional modular expandable irrigation controllers also provide multiple sensor interface, network communications, and flow sensing capabilities. The microprocessor in such systems can quickly become overloaded. This in turn limits the functionality of one or more of the tasks performed by the irrigation controller and limits the future addition of new functional features.